1. Field of the Invention
The present invention relates to a production apparatus of a multilayer coating film, and particularly to a production apparatus of a multilayer coating film which produces function films such as a wide view angle film and an antireflection film that are used for liquid crystal displays.
2. Description of the Related Art
Recently, various kinds of function films such as a wide view angle film and an antireflection film are widely used for a liquid crystal display. This function film needs to have a small film thickness, no adherence of dust to a coating surface, no coating fault such as a level variation and a streak, and no drying fault such as unevenness on the surface induced by drying-wind, and it further needs to have a high quality coating surface with a coating thickness deviation of 3% or less. The function film comprises multiple coating layers, and the multiple coating layers are made by applying coating solutions with organic solvents a plurality of times to a flexible substrate (hereinafter referred to as a web).
Since the above-described high quality is demanded, the function film with the high quality coating surface cannot be efficiently produced with an ordinary coating device. For example, with a coating device equipped with one coater and a dryer, a web has to be repeatedly passed through the coating device as many times as the number of layers to perform multilayer coating, thus causing the disadvantage that a large variation occurs to the quality, and production efficiency becomes extremely low. Only in terms of quality, it is considered to perform multilayer coating with a spattering device, but the production speed is extremely low with 1 m/min, and the production cost is too high, thus making it difficult to be adopted. There is a multilayer coating apparatus for performing multilayer coating by placing a plurality of sets of coating devices including coaters and dryers in layers, where a web is continuously transferred from the coating device on the upper layer to the coating device in the lower layer to perform multilayer coating. However, the multilayer coating apparatus is limited to three layer coating at the maximum in terms of operability because a delivery device and a winder for the web should not be far from the coater. This apparatus has the disadvantage that a burden of cleaning the coating devices, an operation of passing the web through the devices and the like is too large, and too much loss of time concerning the maintenance is required.
From the viewpoint of efficient multilayer coating, a gravure printing apparatus having three sets to ten sets or more at the maximum of coaters and dryers for one printing apparatus is the most efficient apparatus.
However, in the gravure printing apparatus, it is difficult to build a preferable and flexible coating construction corresponding to the number of layers of the multiple coating layers, and the gravure printing apparatus is insufficient as a multilayer coating film production apparatus for a function film which is demanded to have the above-described high quality in terms of coating, drying, dust prevention and handling. Accordingly, the fact is that there is no production apparatus of the multilayer coating films, especially, no preferable production apparatus of the multilayer coating films which efficiently produces high quality function films such as wide view angle films and antireflection films used for liquid crystal displays.